A major challenge of oncology surgery is removing cancer cells from the tumor bed with certainty. Residual cancer, which refers to cancer cells left behind after the initial resection surgery, can lead to local recurrence, increased rates of metastasis, and poorer outcomes. Currently, there is a high rate of secondary surgeries because cancer cells are found at the margins of the resected mass during post-operative pathological analysis of the tumor. For example, 50% of breast conserving lumpectomies (Mullenix et al., Am. J. Surg., 187:643-646, 2004), 35% of limb-sparing sarcoma surgeries (Zornig et al., Br. J. Surg., 82:278-279, 1995), and 37% or radical prostatectomies (Vaidya et al., Urology, 57:949-954, 2001) fail to completely remove cancer cells during the initial surgery. One of the leading causes of not being able to remove all the cancer cells in the tumor bed is the lack of an intraoperative visualization technology that can guide the surgeon to identify and remove the diseased cell. In many cases, effective and total resection of cancers in organs is further complicated because essential adjacent structures need to be spared (for example brain surgeries or other surgeries where important nerves or blood vessels are nearby).
Standard assessment of a resection is performed by inking the outside of the excised tissue, freezing it and then examining the edge of specimen sections by light microscopy (known as frozen section analysis). The presence of tumor cells at the inked margin, which is referred to as a positive margin, indicates that tumor cells remain behind in the tumor bed. Although margin assessment of a frozen section can take place during surgery, time constraints normally limit this assessment to small areas of the tumor. Therefore, this approach is prone to sampling error. The remaining excised tissue is fixed in formalin and it may take several days before the pathologist can complete the analysis to identify a positive margin. If a positive margin is identified, patients most often require a repeat surgical resection, leading to increased patient morbidity and higher healthcare costs. Other intraoperative cancer detection technologies have been developed including radio-frequency (RF) spectroscopy analysis of the surface of resected tumors (Allweis et al., Am. J. Surg., 187:643-646, 2004), Raman and elastic scattering spectroscopy (Bigio et al., J. Biomed. Opt. 5:221-228, 2000) and tissue autofluorescence (Demos et al., J. Biomed. Opt., 9:587-592, 2004). However, each of these technologies lacks the resolution, sensitivity and ease of use required for rapid assessment of microscopic residual cancer within the entire tumor and does not provide means of tissue removal.
A common method used to destroy cells in situ is laser ablation therapy. Laser ablation therapy refers to the destruction of tissue by delivering heat in the form of light into a small volume. Typically, the laser light is presented in short pulses to reduce damage and overheating of surrounding healthy tissue. The amount of tissue being ablated is controlled by the size of the laser focal spot (0.2-3 mm in diameter), intensity and duration of exposure. At the focal spot, temperatures will reach 100° C. which causes vaporization of the tissue due to evaporation of interstitial water (Gough-Palmer et al., Laryngoscope, 116:1288-1290, 2006). At about 1.5 diameters, temperatures reaching 50° C.-54° C. will induce instant cell death, rapid coagulative necrosis, and immediately cauterize the wound limiting the blood loss to a minimum (Goldberg et al., Acad. Radiol., 3:212-218, 1996).
To reach the desired depth of ablation, the wavelength of the laser light has to be carefully chosen. For example, a potassium titanyl phosphate laser (KTP) producing light at a 532 nm wavelength is typically used for ablation of tissue limited to surface treatment (for example, skin cancer and tumors at the periphery of organs), as its depth of penetration is only 900 μm. Carbon dioxide lasers are also used for surface ablation as its 10.6 μm wavelength is heavily absorbed by water inside tissue limiting its penetration depth to approximately 300 μm. For ablation of diseased tissue below the surface, Nd:YAG lasers, operating at a wavelength of 1064 nm, provide penetration depths up to 15 mm (Reinisch, Otoralyngol. Clin. North. Am., 29:893-914, 1996).
Laser ablation procedures are usually non- or minimally-invasive and guided by standard imaging techniques. Currently, laser ablation has been used intraoperatively to remove visible cancer nodes in lung tumors, unresectable liver metastasis, small breast cancers and laryngeal cancers. However, ablation therapy lacks cellular resolution because it is often limited by the spatial resolution provided by the guiding imaging techniques; thus, it can easily leave millions of cancer cells behind. For example, the Gamma Knife unit used in brain surgery has a theoretical accuracy of 0.2 mm but it is limited by the imaging resolution of 2 mm and positioning and excision accuracy of the surgeon.
Thus, a need exists for an intraoperative and real-time cancer cell detection and therapy device at a single-cell level to ensure thorough examination of the tumor bed for residual cancer while providing guidance for additional tissue removal. A single-cell image detection technology could be used to guide an automatic cell ablation system to destroy the cancer cells as soon as they are detected. The combined system will give the surgeon the ability to remove cancer cells at an unprecedented single cell level while providing a minimum impact on the healthy tissue. This will address the difficulty of removing residual cancer in complicated open and endoscopic surgeries such as brain, sarcoma, and colon.